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occurs(?Simple, ?Term)

Succeeds if Simple is a variable or an atomic type that occurs in the term Term.
Simple
Variable or atomic type.
Term
An arbitrary term.

Description

Succeeds if Simple is a variable, an atom or a number occurring in the term Term.

Modes and Determinism

Fail Conditions

Fails if Simple does not occur in the term Term.

Exceptions

(5) type error
If Simple is neither a variable, an atom nor a number.

Examples

   Success:
   occurs(a,a).
   occurs(X,f(a,b,c,X)).
   occurs(+,f(+,-)).
   occurs(a,[b,c,a,g,a]).
   occurs([ ],[a,b]).
   occurs(1,[A|1]).
   occurs(1.0,[1.0|B]).
   Fail:
   occurs(a,b).
   occurs(X,f(Y,Z)).
   occurs(X,Y).
   occurs(1,"2314").
   occurs([], [a,b|c]).
   Error:
   occurs("str",f("str1","str2","str")). (Error 5)
   occurs([a],[a,b]).                    (Error 5)
   occurs(f(a,b),f(a,b)).                (Error 5)

See Also

instance / 2, variant / 2